Typically you'll use a roller for large flat wall areas and a paint brush for "cutting in." Cutting in is a term used to describe painting the corners at walls and ceilings and around baseboards and door/window trim. The wall areas not cut-in would then be painted with a roller or paint brush. The paint brush is typically used to cut-in because it gives you the most control.
- If you are right handed, cut in the wall at the ceiling corners from left to right. If left handed, paint right to left. This will give you visual control over how well the paint is flowing.
- Press the brush against the wall just enough to flex the bristles and use the narrow edge of the paint brush when cutting in.
- Convention has it that if the cut-in corner has two colors (wall / ceiling for example), then the lighter color paint would extend into the darker color area slightly and the darker color would be cut -in and painted on top of the lighter color. This way you don't have to worry about the lighter color not covering and reading the darker color underneath.